1. Field of the Invention
The present invention relates to a vocal sound input apparatus mounted in an automotive vehicle and relates especially to a mounting structure of both of a talk receiving microphone and a noise collecting microphone on the automotive vehicle.
2. Description of the Related Art
A telephone hand-free apparatus has been known as an automotive telephone system which is capable of carrying out a telephone conversation while a vehicle driver drives the vehicle. In the telephone hand-free apparatus, a microphone to input a vocal sound of a speaker and a speaker to output a vocal sound of a telephone conversation party are disposed within a passenger compartment of the vehicle. By connecting a portable (or cellular) telephone to the telephone hand-free apparatus, the telephone conversation can be carried out while the vehicle driver grasps a steering wheel of the vehicle, as disclosed in a Japanese Patent Application First Publication No. 2001-119450 published on Apr. 27, 2001. In addition, a voice recognition operation system has been proposed which controls a vehicle mounted equipment such as a car navigation device. In a conventional voice recognition operation system, a microphone to input a vocal sound of an operator is disposed within the passenger compartment. The vocal sound inputted to this microphone can operate various vehicle mounted pieces of equipment as a control command, as disclosed in a Japanese Patent Application First Publication No. 2002-123283 published on Apr. 26, 2002 (which corresponds to a United States Patent Application Publication No. US2002/0046033 published on Apr. 18, 2002).
In such a vehicle mounted telephone apparatus or vehicle mounted vocal sound recognition apparatus as described above, it is necessary to receive and recognize the vocal sound accurately even if a surrounding noise is large during a high-speed travel of the vehicle. In general, if the vehicle makes a high-speed travel, a traveling noise becomes large and S/N ratio (a signal-to-noise ratio) becomes worsened. An accurate vocal sound reception becomes difficult. Hence, it is necessary to devise a layout (for example, the microphone is disposed in the proximity to a speaker) so that a signal level is maintained at a high level. Furthermore, as a technology of maintaining the S/N ratio, the noise is collected by means of another telephone and accommodated to the input of the speaking microphone only to eliminate the noise components has been proposed. A phase of the noise is inverted to synthesize an original signal (vocal sound signal mixed with a noise) so that a noise cancel mechanism has been proposed in which only noise component is cancelled to obtain a desired signal (refer to a Japanese Patent Application First Publication No. Heisei 10-210131 published on Aug. 7, 1998.